Recently, because of the prosperity of various industries and businesses, the demand for electric power has been increasing. Moreover, rises in the standard of living and changes in the lifestyle are leading to a shortage of power sources. The shortage can be dealt with by developing new power sources or conserving electric power. Nevertheless, to develop a new power source is a long-term task. On the other hand, exploiting other energy options is easily accomplished within a short time. Among these options, one is to replace electric power with a non-electric power. For instance, an air-conditioner is driven by a gas-powered device instead of an electric-powered device. This can reduce peak electric power load. Meanwhile, the saved electric power can be used to further reduce the power consumed by other devices. Such versatile use of various energy sources can result in a substantial saving of energy. It is also helpful for balanced management of overall energy resource. To save energy means to efficiently utilize it. Among all kinds of power consumed in various applications, the growth rate of the electric power consumed by air-conditioners is the most rapid. It is also the major cause of power shortages. However, to drive the air-conditioner by other energy sources except electric power is one of the versatile applications of energy. Especially, one of the most potential air-conditioning equipments is a gas-powered engine-driven heat pump. The gas-powered engine-driven heat pump has the advantage of the efficient utilization of energy sources.